Method of forming semiconductor patterns

ABSTRACT

Semiconductor patterns are formed by performing trimming simultaneously with the process of depositing the spacer oxide. Alternatively, a first part of the trimming is performed in-situ, immediately before the spacer oxide deposition process in the same chamber in which the spacer oxide deposition is performed whereas a second part of the trimming is performed simultaneously with the process of depositing the spacer oxide. Thus, semiconductor patterns are formed reducing PR footing during PR trimming with direct plasma exposure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/323,918, filed on Apr. 14, 2010, in the United States Patent andTrademark Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method of forming semiconductorpatterns. More specifically, the present invention relates to a spacerdefined double patterning (SDDP) process using a PEALD spacer oxidedeposition process having trimming action.

(b) Description of the Related Art

Due to the limit of resolution of the immersion ArF lithography, themethod of Double Patterning is used in the chip patterning process for3× nm half pitch and below.

In the art, the method of Spacer Defined Double Patterning, asrepresented in FIGS. 1A-1D, is as follows. As shown in FIG. 1A, photoresist template patterns 2 are formed on top of a bottom layer 1. Here,the line width and the line spacing are in a ratio of about 1:3. Asshown in FIG. 1B, an oxide spacer conformal 3 is deposited on the photoresist template patterns 2. Here, the thickness of the oxide film isequal to the width of template line.

Next, as shown in FIG. 1C, the deposited spacer oxide film 3 is etchedback by RIE (reactive ion etching) such that film on the upper andbottom surfaces of pattern are removed and spacers 3 a are formed on theside wall surfaces of the photo resist template patterns 2.

Then, as shown in FIG. 1D, the photo resist template patterns 2remaining between the spacers 3 a are removed by selective etching andthe bottom layer 1 is etched by using the spacers 3 a as hard mask.

As single exposure lithography is very challenging in achieving 3× nmline widths and below, in the art a photo resist shrink step can beapplied prior to the deposition of the spacer material as shown in FIG.2A to FIG. 2E. Firstly, first photo resist template patterns 22 areformed on top of a bottom layer 11 as shown in FIG. 2A. Here, the ratioof line width X1 to spacing in between the lines of the first photoresist template patterns 22 is 1: A, wherein 1≦A<3. The photo resisttemplate patterns 22 are trimmed so that the line width of the photoresist template patterns 22 shrinks to form the second photo resisttemplate patterns 22 a as shown in FIG. 2B. Here, the line width X2 isabout ⅓ of the line spacing of the second photo resist template patterns22 a. The trimming can be performed by an oxygen plasma or by thermalannealing in an inert ambient or in an oxidizing or reducing ambient.The trimming can be performed in a separate chamber or in-situ, in thesame chamber in which the spacer oxide deposition is performed withoutremoving the substrate from the chamber in between the trimming anddeposition steps.

As shown in FIG. 2C, an oxide spacer conformal 33 is deposited on thesecond photo resist template patterns 22 a. Here, the thickness of theoxide film 33 is equal to the width of the second photo resist templatepatterns 22 a. The deposited spacer oxide film 33 is etched back by RIE(reactive ion etching) such that the film 33 on the upper and bottomsurfaces of patterns 22 a are removed and film on the side wall surfacesof the patterns 22 a remain to be spacers 33 a as shown in FIG. 2D.Then, as shown in FIG. 2E, the second photo resist template patterns 22a remaining between spacers 33 a are removed by selective etching sothat the spacers 33 a remain and then the bottom layer 11 is patternedby using the spacers 33 a as a hard mask (HM).

Through the above described sequence, the number of lines having thesame width as the lines of the template after trimming is doubled andthe pitch is halved. Instead of a spacer oxide, an alternative material,such as an oxynitride or a nitride material with suitable properties,could be selected.

If the target Critical Dimension of lines is getting smaller than 30 nm,it will become difficult to control the uniformity of the amount ofshrinking of such a photo resist shrink step or trimming step.Furthermore, there is a higher chance of patterning failure due to theleaning or collapsing of photo resist line due to the weak footing ofthe photo resist line when the photo resist line becomes narrower by thetrimming.

SUMMARY OF THE INVENTION

The purpose of the invention is to secure measures to solve the problemswhich could occur in performing such a trimming step and to provide aSpacer Defined Double Patterning processes for 3× nm and below thatavoids the problems discussed above.

To solve the problems, trimming is performed simultaneously with theprocess of depositing the spacer oxide. In an alternative embodiment, afirst part of the trimming is performed in-situ, immediately before thespacer oxide deposition process in the same chamber in which the spaceroxide deposition is performed whereas a second part of the trimming isperformed simultaneously with the process of depositing the spaceroxide. The present invention also provides a method to reduce PR footingduring PR trimming with direct plasma exposure.

In an embodiment of the invention, trimming is performed simultaneouslywith the process of depositing the spacer oxide. The spacer oxidedeposition process is a Plasma Enhanced Atomic Layer Deposition process.

In another embodiment of the invention, a first part of the trimming isperformed in-situ, immediately before the spacer oxide depositionprocess in the same chamber in which the spacer oxide deposition isperformed whereas a second part of the trimming is performedsimultaneously with the process of depositing the spacer oxide. Thefirst part of the trimming is preferably performed by a continuousoxygen plasma or by a pulsed oxygen plasma. The spacer oxide depositionprocess is a Plasma Enhanced Atomic Layer deposition process.

In another embodiment of the invention, PR trimming process under directplasma makes PR footing reduce. This process includes two steps: a firststep of PR trimming under direct plasma environment without supplying aprecursor, a second step of deposition of SiO₂ film. In a direct plasmagenerated between a susceptor electrode grounded on earth on which thesubstrate is placed and an opposing electrode such as a shower headelectrode, activated ions are accelerated in a vertical directiontowards the substrate placed on the susceptor electrode and lead tohigher trimming rate towards vertical direction than horizontaldirection on the PR so that PR footing remaining in the bottom of PR isreduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describingembodiments thereof in detail with reference to the accompanying drawingin which:

FIG. 1A to FIG. 1D show a Prior Art method of Spacer Defined DoublePatterning without trimming.

FIG. 2 a to FIG. 2E show a Prior Art method of Spacer Defined DoublePatterning with trimming prior to spacer deposition.

FIG. 3A to FIG. 3D show an embodiment of the present invention whereintrimming is preformed during the deposition of the spacer oxide.

FIG. 4A to FIG. 4E show another embodiment of the present inventionwherein trimming is performed both prior to and during the deposition ofthe spacer oxide.

FIG. 5A to FIG. 5C show yet another embodiment of the present inventionwherein PR trimming and PR footing reduction are performedsimultaneously prior to the deposition of the spacer oxide.

FIG. 6 shows process sequence according to FIGS. 5A-5C.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art would realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

FIG. 3A to FIG. 3D show an embodiment of the present invention whereintrimming is simultaneously preformed during the deposition of the spaceroxide. As shown in FIG. 3A, first photo resist or carbon based materialtemplate patterns 120 are on top of a bottom layer 110. Here, the ratioof line width XX to line spacing of the first photo resist templatepatterns 120 is 1: A (1≦A<3).

As shown in FIG. 3B, a spacer oxide film 130 is deposited on the formedfirst photo resist template patterns 120 and simultaneously second photoresist template patterns 120 a having a width XX2 and a height Y2 thatis smaller than the width XX and the height Y of the first photo resisttemplate patterns 120 are formed, using a Plasma Enhanced Atomic LayerDeposition process using sequential and alternating pulses of source gassuch as a silicon precursor and reactant such as O₂ plasma. In thisstep, the O₂ plasma should be provided with a condition that: (i) thefirst template patterns 120 can be etched with a certain etching ratesuch that the first photo resist template patterns 120 are trimmed toform the second photo resist template patterns 120 a and (ii) oxygenradical can be reacted with a precursor deposited previously on thesubstrate to form the spacer oxide film 130 such as SiO₂ film by PEALDmethod. At the end of this step, a ratio of the line width to linespacing of the second photo resist template patterns 120 a should be 1:3and the thickness of the deposited spacer oxide film 130 should be equalto the width of the second photo resist template patterns 120 a. The O₂plasma may be a direct plasma wherein the plasma is generatedimmediately adjacent to the substrate or a remote plasma.

Then, the deposited spacer oxide film 130 is etched back by RIE suchthat the deposited spacer oxide film 130 on the upper and bottomsurfaces of patterns 120 a is removed and the deposited spacer oxidefilm 130 on the side wall surfaces of the patterns 120 a remains to bespacers 130 a as shown in FIG. 3C.

Subsequently, as shown in FIG. 3D, the second photo resist templatepatterns 120 a remaining between the spacers 130 a are removed byselective etching such that the spacers 130 a remain. Then, the bottomlayer 110 is patterned by using the spacers 130 a as a hard mask (HM).

FIG. 4A to FIG. 4E show another embodiment of the present inventionwherein trimming is simultaneously preformed during the deposition ofthe spacer oxide film. Firstly, as shown in FIG. 4A, first photo resistor carbon based material template patterns 120 are formed on top of abottom layer 110. Here, the ratio of line width XX to spacing in betweenthe lines of the first photo resist template patterns 120 is 1: A(1≦A<3).

Next, as shown in FIG. 4B, the first photo resist template patterns 120are firstly trimmed so that the line width shrinks to form third photoresist template patterns 120 aa having a line width XX1 (whereinXX1<XX). Here, the ratio of line width XX1 to spacing in between thelines of the third photo resist template patterns 120 aa is 1: B(wherein A<B<3). The first trimming can be performed by an oxygen plasma(direct plasma or remote plasma) or by thermal annealing in an inertambient or in an oxidizing or reducing ambient. Preferably, the firsttrimming is performed in-situ, in the same chamber in which the spaceroxide deposition is performed without removing the substrate from thechamber between the trimming and deposition steps.

Next, as shown in FIG. 4C, a spacer oxide film 130 is deposited on thethird photo resist template patterns 120 aa and the third photo resisttemplate patterns 120 aa are simultaneously secondly trimmed so thatfourth photo resist template patterns 120 b having a width XX2 and aheight Y2 that is smaller than the width XX1, the height Y of the firstphoto resist template patterns 120, and the height Y1 of the third photoresist template patterns 120 aa are formed, using a Plasma EnhancedAtomic Layer Deposition process using sequential and alternating pulsesof source gas such as a silicon precursor and reactant such as O₂plasma. In this step, the O₂ plasma should be provided with a conditionthat: (i) the third template patterns 120 aa can be etched with acertain etching rate such that the third template patterns 120 aa aretrimmed to form the fourth photo resist template patterns 120 b and (ii)oxygen radical can be reacted with precursor deposited previously on thesubstrate to form the spacer oxide film 130 such as SiO₂ film by PEALDmethod. At the end of this step, the photo resist pattern lines haveshrunk to a width XX2 (wherein XX2<XX1) and the ratio of line width XX2to line spacing should be 1:3 and the thickness of the deposited spaceroxide film 130 should be equal to width XX2 of the fourth photo resisttemplate patterns 120 b. Here, the O₂ plasma may be a direct plasma or aremote plasma.

As shown in FIG. 4D, the deposited spacer oxide film 130 is etched backby RIE such that the film 130 on the upper and bottom surfaces of thefourth photo resist template patterns 120 b are removed and the film 130remains on the side wall surfaces of the fourth photo resist templatepatterns 120 b to be spacers 130 a.

As shown in FIG. 4E, the fourth photo resist template patterns 120 bremaining between the spacers 130 a are removed by selective etchingsuch that the spacers 130 a remain. Then, the bottom layer 110 ispatterned by using the spacers 130 a as a hard mask (HM).

The trimming of the photo resist template patterns during the PEALDprocess of the spacer oxide film might occur in particular during theinitial cycles of the deposition process. When multiple cycles of thespacer oxide have been deposited, the photo resist template patternsmight be protected from the O₂ plasma so that further etching andshrinking of the photo resist does not occur anymore and only spaceroxide deposition occurs. The conditions of the spacer oxide depositionprocess and an eventual trimming step prior to the spacer oxidedeposition should be selected such that after completion of the spaceroxide template: line width=line space=film thickness.

Experimental Example 1

A SiO₂ film deposition by PEALD on photo resist template patterns iscarried out with the following conditions.

Metalorganic precursors or halosilane precursors containing Si can beused as Si precursors. In the present invention, for example,SiH₂[N(C₂H₅)₂]₂ was used as a Si precursor. Susceptor temperature forheating substrate varied from room temperature to 200 degree C.,preferably the susceptor temperature was 50 degree C. During deposition,process pressure is maintained in a range from 1 to 10 Torr, preferablyat a value of about 3 Torr. RF plasma power is in a range from 10 to1000 W, preferably at a value of about 200 W.

Gas flow condition is as follows.

-   -   Source Ar flow rate for carrying bubbled precursor into reactor:        200 sccm    -   Temperature of precursor container: 60° C.    -   O₂ reactant flow rate: 50 sccm    -   Reactant Ar flow rate for flowing into reactor with oxygen: 200        sccm    -   Main Ar flow rate for chamber/gas line purge: 200 sccm

Process time per cycle is as follows.

-   -   Source feeding/Purge/Plasma/Purge=1.0/1.0/0.3/1.0 (unit: second)

In the above sequence, oxygen is continuously provided during all stepsof the cycle and activated when plasma is provided. When not activatedby the plasma, the oxygen is not reactive and just acts as a purge gas.In an alternative embodiment, the oxygen can also be providedintermittently, synchronously with the plasma pulses. The above cycle isrepeated until a target thickness is achieved. The deposited filmthickness per cycle is about 0.12 nm.

For a photo resist trimming step prior to the PEALD deposition step,similar conditions can be used as during the PEALD step but withoutflowing the Silicon precursor. The photo resist film thickness reductionfor a blanket photo resist layer would be about 0.25 nm per cycle. Then,after a number of cycles comprising oxygen plasma pulses resulting in aninitial thinning of the photo resist lines, the Silicon precursor flowcan be switched on and some additional photo resist line width reductioncan be obtained during the PEALD deposition step. In a first example,the width of the photo resist lines, or critical dimension (CD) directlyafter lithography is 40 nm and the line spacing is also 40 nm. During anin-situ trimming step prior to deposition, a CD reduction down to 25 nmis achieved. In a subsequent spacer deposition step of 20 nm thickness,an additional reduction of the CD from 25 nm down to 20 nm is achieved.In a second example, the critical dimension of the photo resist lines is30 nm directly after lithography and the line spacing is 30 nm. Duringan in-situ trimming step prior to a spacer deposition step, a reductionof photo resist CD down to 20 nm is achieved. Then, during a 15 nmspacer oxide PEALD step, a further reduction of photo resist CD from 20nm down to 15 nm is achieved.

FIG. 5A to FIG. 5C show yet another embodiment of the present inventionwherein PR trimming and PR footing reduction are performedsimultaneously prior to the deposition of the spacer oxide. Thisembodiment is similar to the embodiment described right above. However,this embodiment further includes reduction step of PR (photo resist)footing prior to spacer oxide film deposition.

As shown in FIG. 5A, PR (photo resist) footing in the lower portions ofthe photo resist template pattern may be generated. During the trimmingstep, the PR pattern is exposed to a direct plasma in a PR footingreduction step so that activated ions like O₂ radical or Ar radical areaccelerated towards the vertical direction, so trimming rate in thevertical direction (perpendicular to substrate and to electrode) isfaster than in the horizontal direction (parallel to electrode) as shownin FIG. 5B. Therefore, the photo resist (PR) footing is reduced as shownin FIG. 5C. In this embodiment, the line width of the photo resisttemplate patterns and the spacing between lines of the photo resisttemplate patterns are in a ratio of 1:C (wherein 1<C<3). In the exampleshown in FIG. 5C, C is about 1. This PR footing reduction step by directplasma exposure results, in addition to footing reduction, to PRtrimming and can also be considered as a PR resist trimming step withimproved characteristics. This process is performed in the same reactorchamber as wherein deposition is performed. If the PR footing has beenadequately removed in the PR footing reduction step, but additionaltrimming is needed, an additional trimming step without direct plasmaexposure can be performed, either before or after the PR reduction stepbut prior to deposition.

Experimental Example 2

A SiO₂ film deposition by PEALD on photo resist template patterns iscarried out with the following conditions.

Metalorganic precursors or halosilane precursors containing Si can beused as Si precursors. In this invention, SiH₂[N(C₂H₅)₂]₂ was used as aSi precursor. Susceptor temperature for heating substrate varied fromroom temperature to 200 degree C., preferably the susceptor temperaturewas 50 degree C. During deposition, process pressure is maintained in arange from 1 to 10 Torr, preferably at a value of about 3 Torr. RFplasma power is in a range from 10 to 1000 W, preferably at a value ofabout 100 W to 150 W.

Gas flow condition:

-   -   Source Ar flow rate for carrying bubbled precursor into reactor:        500 sccm    -   Temperature of precursor container: 60° C.    -   O₂ reactant flow rate: 1000 sccm    -   Reactant Ar flow rate for flowing into reactor with oxygen: 500        sccm    -   Main Ar flow rate for chamber/gas line purge: 200 sccm    -   Reaction space gap between showerhead and substrate: 14.5 mm.

Processing time:

-   -   Pre-trimming step: <2.0 sec.    -   Deposition step time: <2.0 sec.    -   Plasma pulsing time: 0.2 sec    -   Purge time: 1.0 sec.

FIG. 6 shows process sequence according to FIGS. 5A to 5C. Cycle forpre-trimming step for PR footing reduction is repeated and deposition isperformed after that. Reactant like O₂ is provided during thepre-trimming step and deposition step. Purge gas like Ar is providedduring the deposition step. Plasma is provided intermittently during thepre-trimming step and deposition step.

The advantages of the present invention are as follows, compared to thecase of performing trimming separately in advance.

If the template pattern (PR or carbon-based film) is trimmed to a widthof 1× (10 to 19 nm) in a separate etching chamber, the reduction ofwidth to height could lead to the weakening of the geometric structure,so the template pattern line could easily lean or collapse in thecleaning or wafer handling process after trimming. However, if thetrimming and the film deposition are performed simultaneously accordingto the above described embodiments of the present invention, thedeposited film can support the template pattern and the template patterncan maintain its shape or structure even if the width of the templatepattern is thinned to the level of 10 nm.

Combining the trimming and the deposition process results in a simplerand more efficient process.

In ALD, the coverage of deposited material on the substrate changesgradually from 0% to 100% (full coverage) along the number of depositioncycles. As the coverage changes along the deposition, the simultaneouslyetching of a layer on which the spacer oxide film is deposited (photoresist or carbon template patterns in this invention) reduces and theapparent etching rate decelerates from a certain etching rate to zeroetching rate. This deceleration of etching rate would help to controlthe very fine CD of the photo resist template patterns or carbon line.In prior art of dry etching, it would be very difficult to control theetching amount precisely with controlled time. If the overall etchingrate is low, it would impact on the productivity, and if the etchingrate is fast, it would impact on the controllability of CD. But,according to the present invention, by implementing the simultaneousetching and deposition, the sufficient etching rate at initial stage andsufficient controllability of CD can be achieved due to the variation ofetching rate from high to low (deceleration effect) as the spacer oxidecoverage gets close to the full coverage starting from zero coverage.

PR trimming process under direct plasma prior to deposition step leadsto the reduction of PR footing as activated species is accelerated moretowards the vertical direction than the horizontal direction on PR sothat trimming rate is faster in the vertical direction than thehorizontal direction on PR. This leads to better trimming and improvesfilm uniformity in the deposition step.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A method of forming semiconductor patterns, the method comprising:forming a photo resist template having a pattern of lines on a bottomlayer, the pattern having a line width and a line spacing, the ratio ofthe line width to the line spacing being 1: A wherein 1≦A<3; depositinga spacer oxide conformal over the photo resist template by a PlasmaEnhanced Atomic Layer deposition process, using sequential andalternating pulses of a silicon precursor and an oxygen plasma, suchthat trimming of the photo resist template occurs and the ratio of theline width to the line spacing becomes 1:3 and the thickness of thedeposited spacer oxide is about equal to the trimmed line width; etchingback the deposited spacer oxide such that spacer oxide films on upperand bottom surfaces of the pattern are removed, with spacer oxide filmson side wall surfaces of the photo resist template remaining; removingthe photo resist template remaining between the spacer oxide films byselective etching; and patterning the bottom layer by using theremaining spacer oxide films formed as mask.
 2. The method of claim 1,further comprising: trimming, prior to the step of depositing the spaceroxide, the photo resist pattern of lines such that the ratio of the linewidth to the line spacing becomes 1: B, wherein A<B<3 by exposing thephoto resist pattern of lines to pulses of the oxygen plasma, in thesame reaction chamber in which the spacer oxide deposition is performed.3. The method of claim 2, further comprising: a PR footing reductionstep prior to the step of depositing the spacer oxide, in the samereaction chamber in which PR trimming step and the spacer oxidedeposition step are performed, the PR footing reduction step comprisinga direct plasma exposure step.
 4. The method of claim 3, wherein the PRfooting reduction step is performed prior to the PR trimming step. 5.The method of claim 3, wherein the PR footing reduction step isperformed after the PR trimming step.
 6. The method of claim 1, whereinthe plasma is a direct plasma.
 7. The method of claim 1, wherein theplasma is a remote plasma.
 8. The method of claim 2, wherein the plasmais a direct plasma.
 9. The method of claim 2, wherein the plasma is aremote plasma.
 10. The method of claim 1, wherein the silicon precursoris SiH2[N(C2H5)2]2.